The control of neural stem cells by morphogenic signals

A complex orchestration of stem-cell specification, expansion and differentiation is required for the proper development of the nervous system. Although progress has been made on the role of individual genes in each of these processes, there are still unresolved questions about how gene function translates to the dynamic assembly of cells into tissues. Recently, stem-cell biology has emerged as a bridge between the traditional fields of cell biology and developmental genetics. In addition to their potential therapeutic role, stem cells are being exploited as experimental 'logic chips' that integrate information and exhibit self-organizing properties. Recent studies provide new insights on how morphogenic signals coordinate major stem cell decisions to regulate the size, shape and cellular diversity of the nervous system.     

Light sheet microscopy for real-time developmental biology

Within only a few short years, light sheet microscopy has contributed substantially to the emerging field of real-time developmental biology. Low photo-toxicity and high-speed multiview acquisition have made selective plane illumination microscopy (SPIM) a popular choice for studies of organ morphogenesis and function in zebrafish, Drosophila, and other model organisms. A multitude of different light sheet microscopes have emerged for the noninvasive imaging of specimens ranging from single molecules to cells, tissues, and entire embryos. In particular, developmental biology can benefit from the ability to watch developmental events occur in real time in an entire embryo, thereby advancing our understanding on how cells form tissues and organs. However, it presents a new challenge to our existing data and image processing tools. This review gives an overview of where we stand as light sheet microscopy branches out, explores new areas, and becomes more specialized.     

Rice plant development: from zygote to spikelet

Rice is becoming a model plant in monocotyledons and a model cereal crop. For better understanding of the rice plant, it is essential to elucidate the developmental programs of the life cycle. To date, several attempts have been made in rice to categorize the developmental processes of some organs into substages. These studies are based exclusively on the morphological and anatomical viewpoints. Recent advancement in genetics and molecular biology has given us new aspects of developmental processes. In this review, we first describe the phasic development of the rice plant, and then describe in detail the developmental courses of major organs, leaf, root and spikelet, and specific organs/tissues. Also, for the facility of future studies, we propose a staging system for each organ.     

Ringing in the new ear: resolution of cell interactions in otic development

The vertebrate inner ear is a marvel of structural and functional complexity, which is all the more remarkable because it develops from such a simple structure, the otic placode. Analysis of inner ear development has long been a fascination of experimental embryologists, who sought to understand cellular mechanisms of otic placode induction. More recently, however, molecular and genetic approaches have made the inner ear a useful model system for studying a much broader range of basic developmental mechanisms, including cell fate specification and differentiation, axial patterning, epithelial morphogenesis, cytoskeletal dynamics, stem cell biology, neurobiology, physiology, etc. Of course, there has also been tremendous progress in understanding the functions and processes peculiar to the inner ear. The goal of this review is to recount how historical approaches have shaped our understanding of the signaling interactions controlling early otic development; to discuss how new findings have led to fundamental new insights; and to point out new problems that need to be resolved in future research.     

Induction and patterning of the cardiac conduction system

The cardiac conduction system (CCS) is the component of the heart that initiates and maintains a rhythmic heartbeat. As the embryonic heart forms, the CCS must continue to develop and mature in a coordinated manner to ensure that proper pace making potential and distribution of action potential is maintained at all stages. This requires not only the formation of distinct and disparate components of the CCS, but the integration of these components into a functioning whole as the heart matures. Though research in this area of development may have lagged behind other areas of heart development, in recent years there has been much progress in understanding the ontogeny of the CCS and the developmental cues that drive its formation. This is largely due to studies on the avian heart as well as the use of molecular biology approaches. This review gives a perspective on advances in understanding the development of the vertebrate CCS, and reports new data illuminating the mechanism of conduction cell determination and maintenance in the mammalian heart. As much of our knowledge about the development of the CCS has been derived from the chick embryo, one important area facing the field is the relationship and similarities between the structure and development of avian and mammalian conduction systems. Specifically, the morphology of the distal elements of the mammalian CCS and the manner in which its components are recruited from working cardiomyocytes are areas of research that will, hopefully, receive more attention in the near future. A more general and outstanding question is how the disparate components of all vertebrate conduction systems integrate into a functional entity during embryogenesis. There is mounting evidence linking the patterning and formation of the CCS to instructive cues derived from the cardiac vasculature and, more specifically, to hemodynamic-responsive factors produced by cardiac endothelia. This highlights the need for a greater understanding of the biophysical forces acting on, and created by, the cardiovascular system during embryonic development. A better understanding of these processes will be necessary if therapeutics are to be developed that allow the regeneration of damaged cardiac tissues or the construction of biologically engineered heart tissues.     

Integrative approaches to morphogenesis: lessons from dorsal closure

Although developmental biology has been dominated by the genetic analysis of embryonic development, in recent years genetic tools have been combined with new approaches such as imaging of live processes, automated and quantitative image analysis, mechanical perturbation and mathematical modeling, to study the principles underlying the formation of organisms. Here we focus on recent work carried out on Dorsal Closure, a morphogenetic process during Drosophila embryogenesis, to illustrate how this multidisciplinary approach is yielding new and unexpected insights into how cells organize themselves through the activity of their molecular components to give rise to the stereotyped and macroscopic movements observed during development.     

Embryogenomics: developmental biology meets genomics

Fundamental questions in developmental biology are: what genes are expressed, where and when they are expressed, what is the level of expression and how are these programs changed by the functional and structural alteration of genes? These questions have been addressed by studying one gene at a time, but a new research field that handles many genes in parallel is emerging. The methodology is at the interface of large-scale genomics approaches and developmental biology. Genomics needs developmental biology because one of the goals of genomics – collection and analysis of all genes in an organism – cannot be completed without working on embryonic tissues in which many genes are uniquely expressed. However, developmental biology needs genomics – the high-throughput approaches of genomics generate information about genes and pathways that can give an integrated view of complex processes. This article discusses these new approaches and their applications to mammalian developmental biology.     

Developmental biology of pterobranch hemichordates: history and perspectives

Hemichordates, like echinoderms and chordates, are deuterostomes, and study of their developmental biology could shed light on chordate origins. To date, molecular developmental studies in hemichordates have been confined to the enteropneusts or acorn worms. Here, we introduce the developmental biology of the other group of hemichordate, the pterobranchs. Pterobranchs generally live in cold, deep waters; this has hampered studies of this group. However, about 40 years ago, the colonial pterobranchs Rhabdopleura compacta and R. normani were discovered from shallow water, which has facilitated their study. Using Rhabdopleura compacta from south-west England, we have initiated molecular developmental studies in pterobranchs. Here, we outline methods for collecting adults, larvae, and embryos and demonstrate culturing of larvae under laboratory conditions. Given that the larval and adult forms differ from enteropneusts, we suggest that molecular developmental studies of pterobranchs may offer new insights into chordate origins.     

多能干细胞体外分化为类神经管模型的研究进展

近年来多能干细胞(PSCs)的体外培养与分化技术发展迅速,并广泛应用于再生医学和发育生物学等领域。PSCs能够在体外神经诱导的条件下分化为类神经管模型,这为探索体内早期神经发育与中枢神经系统发育疾病的形成机制提供了全新的实验平台。本文总结了近年来应用小鼠和人PSCs建立体外类神经管模型的研究进展,其中体外模型主要包括在不同培养体系下诱导获得的二维(2D)与三维(3D)类神经管模型,并针对早期类神经管模型在神经系统发育性疾病机制研究中的前景和挑战作进一步探讨,同时为疾病预防和治疗提供新的思路。     

Shining light on Drosophila oogenesis: live imaging of egg development

Drosophila oogenesis is a powerful model for the study of numerous questions in cell and developmental biology. In addition to its longstanding value as a genetically tractable model of organogenesis, recently it has emerged as an excellent system in which to combine genetics and live imaging. Rapidly improving ex vivo culture conditions, new fluorescent biosensors and photo-manipulation tools, and advances in microscopy have allowed direct observation in real time of processes such as stem cell self-renewal, collective cell migration, and polarized mRNA and protein transport. In addition, entirely new phenomena have been discovered, including revolution of the follicle within the basement membrane and oscillating assembly and disassembly of myosin on a polarized actin network, both of which contribute to elongating this tissue. This review focuses on recent advances in live-cell imaging techniques and the biological insights gleaned from live imaging of egg chamber development.     

The Golgi apparatus: Lessons from Drosophila

Historically, Drosophila has been a model organism for studying molecular and developmental biology leading to many important discoveries in this field. More recently, the fruit fly has started to be used to address cell biology issues including studies of the secretory pathway, and more specifically on the functional integrity of the Golgi apparatus. A number of advances have been made that are reviewed below. Furthermore, with the development of RNAi technology, Drosophila tissue culture cells have been used to perform genome-wide screens addressing similar issues. Last, the Golgi function has been involved in specific developmental processes, thus shedding new light on the functions of a number of Golgi proteins.     

Enhancers,development, and evolution

A single-celled fertilized egg develops into a complex, multicellular animal through a series of selection processes of developmental pathways. During these processes, regulatory genes exhibit spatiotemporally restricted expression under the control of the species-specific genetic program, and dictate developmental processes from germ layer formation to cellular differentiation. Elucidation of molecular mechanisms underlying developmental processes and also of mechanistic bases for morphological diversification during evolution is one of the central issues in contemporary developmental biology. Progress has been made due to recent technological innovations, such as high-throughput nucleotide sequencing, live-cell imaging, efficient genetic manipulation, and establishment of the organoid system, opening new avenues to the above issues.     

Chironomid midges: a forgotten model of developmental biology research

For more than a century, embryologists have been exploring various model systems to gain insights into developmental processes. This article presents an overview of the role of chironomid midges in embryology research since their introduction as model organisms in the 19th century. We present the vestiges of bibliography since the days of Weismann (1834–1914), who raised preliminary queries to unravel many unique features of insect embryogenesis using midges as a crucible. Unfortunately, over the years, chironomid midges got lost into obscurity as a model for developmental biology, which is evident from the paucity of developmental biology–related literature on midges in the past decades. Through this essay, the authors intend to share reminiscences of the heydays of chironomid research with the wider community of zoologists with an aim of reviving chironomid embryology. Midges not only possess the basic qualities essential for an ideal model system, but being one of the ancestral dipteran stocks, they can also prove an excellent test system for evo‐devo, transgenetic, and embryogenomic investigations that utilize methodologies at the interface of developmental biology and high‐throughput molecular genetic and genomics approach. An introspection of re‐introducing chironomid midgesas model system will be rewarding for the contemporary developmental biologists.     

Intravital imaging

Until recently, the idea of observing life deep within the tissues of a living mouse, at a resolution sufficient to pick out cellular behaviors and molecular signals underlying them, remained a much-coveted dream. Now, a new era of intravital fluorescence microscopy has dawned. In this Primer, we review the technologies that made this revolution possible and demonstrate how intravital imaging is beginning to provide quantitative and dynamic insights into cell biology, immunology, tumor biology, and neurobiology.     

Phagocytosis: latex leads the way

Phagocytosis is the process that cells have evolved to internalise large particles such as mineral debris, which they store, or apoptotic cells and pathogens, which they have the capacity to kill and degrade. However, several important pathogens can suppress these killing functions and survive and multiply within phagosomes, causing disease. Recent advances in phagosome biology have been made possible largely by a model system that uses inert latex beads. The ability to purify latex bead-containing phagosomes has opened the door to allow comprehensive biochemical analyses and functional assays to study the molecular mechanisms governing phagosome function. These approaches have led to unique insights directly relevant for the understanding of the biology of intracellular pathogens and the ways by which they subvert their hosts.     

Stem cells and regenerative medicine

Stem cells have been defined as clonogenic cells that undergo both self-renewal and differentiation to more committed progenitors and functionally specialized mature cells. Of late years, stem cells have been identified in a variety of tissues of an adult body. Depending on the source, they have the potential to form one or more, or even all cell types of an organism. Stem cell research provided some outstanding contributions to our understanding of developmental biology and offered much hope for cell replacement therapies overcoming a variety of diseases. The establishment of human ES cell lines enabled us to generate all tissues we comprise. Recently, excitement has been evoked by the controversial evidence that adult stem cells have a much higher degree of developmental plasticity than previously imagined. More recently, the existence of multipotent somatic stem cells in bone marrow has been reported. Combined with these discoveries and achievements as well as the developing technologies, scientists are now trying to bring stem cell therapies to the clinic.     

A novel regulatory circuit specifies cell fate in the Arabidopsis root epidermis

The specification of distinct cell fates in multicellular organisms is a fundamental process in developmental biology. The Arabidopsis root epidermis, which consists of root-hair cells and non-hair cells, provides a useful model system for studying cell fate specification. In this tissue, the cell fates are determined by their relative position to the underlying cortical cells, and many genes have been identified that regulate this position-dependent cell fate specification. Recent studies using genetic, molecular, and biochemical approaches have shed new light on this process and revealed a complex network of interacting and interdependent components. In particular, a novel regulatory circuit has recently been identified, which includes a lateral inhibition pathway and a feedback loop that enables intercellular communication and ensures that two distinct cell types arise in an appropriate pattern. This regulatory circuit is also influenced by a positional signaling pathway which includes the SCRAMBLED leucine-rich repeat receptor kinase. The studies of cell fate specification in the Arabidopsis root epidermis provide new insights into the molecular strategies used to define distinct cell types in plants.